1. Field of the Invention
The present invention relates to a driver for driving a fluid pressure pump and a transport mechanism by a common electric motor, and to an automatic pallet changer having such a driver.
2. Description of the Prior Art
Some of machine tools such as machining centers have an automatic pallet changer for exchanging a pallet placed in a machining area where a workpiece is machined and a pallet placed in a working area where a workpiece is attached to and detached from the pallet.
The automatic pallet changer includes a pivot arm, and a driver including a hydraulic unit and a transport mechanism. The hydraulic unit includes a hydraulic cylinder for moving up and down the pivot arm, a hydraulic pump for supplying a working fluid to the hydraulic cylinder, and an electric motor for driving the hydraulic pump. The transport mechanism includes a plurality of gears for driving the pivot arm to pivot the pivot arm, and is driven by a servo motor provided separately from the hydraulic unit.
In the automatic pallet changer, the hydraulic pump is driven by the electric motor to actuate the hydraulic cylinder, whereby the pivot arm is moved up. Thus, the pallets respectively placed in the machining area and in the working area are received and retained by the pivot arm. In turn, the transport mechanism is driven by the servo motor to pivot the pivot arm, whereby one of the pallets is transported from the machining area to the working area and the other pallet is transported from the working area to the machining area. When the other pallet is located above a table in the machining area and the one pallet is located above a support base in the working area, the servo motor is stopped, and then the hydraulic pump is driven by the electric motor to move down the hydraulic cylinder and the pivot arm. Thus, the pallets retained on the pivot arm are respectively placed on the table in the machining area and on the support base in the working area.
In the conventional automatic pallet changer, however, the electric motor for actuating the hydraulic pump and the servo motor for driving the transport mechanism are separately provided. Therefore, the size of the driver and, hence, the size of the automatic pallet changer are increased, making it difficult to reduce the costs thereof. Further, the provision of the two electric motors requires separate driver circuits for controlling these electric motors, thereby preventing cost reduction.
It is an object of the present invention to provide a less expensive driver of a smaller size having a common electric motor for driving a fluid pressure pump and a transport mechanism, and to provide an automatic pallet changer having such a driver.
The driver according to the present invention comprises an actuator, a fluid pressure pump for supplying a working fluid to the actuator, and a transport mechanism for driving a movable body to move the movable body. The driver further comprises a common electric motor for driving the fluid pressure pump and the transport mechanism, and switching means for connecting the electric motor switchably to the fluid pressure pump and to the transport mechanism, wherein one of the fluid pressure pump and the transport mechanism connected to the electric motor is driven by the electric motor.
In the driver, the electric motor is connected to the fluid pressure pump by the switching means when the actuator is to be driven. By driving the fluid pressure pump by the electric motor, the working fluid is supplied to the actuator to drive the actuator. When the movable body is to be moved, the switching means switches the connection of the electric motor from the fluid pressure pump to the transport mechanism to connect the electric motor to the transport mechanism. Then, the transport mechanism is driven by the electric motor to move the movable body. In the driver, the switching means thus switches the connection of the electric motor to connect the electric motor selectively to the fluid pressure pump and to the transport mechanism, so that the fluid pressure pump and the transport mechanism can individually be driven.
In the driver, the fluid pressure pump and the transport mechanism are individually driven by the single common electric motor, which is switchably connected thereto by the switching means. This eliminates the need for providing separate electric motors for the fluid pressure pump and for the transport mechanism, allowing for size reduction and cost reduction of the driver.
The aforesaid driver is advantageously applicable to an automatic pallet changer. That is, the automatic pallet changer comprises: a pivot arm; an actuator for moving up and down the pivot arm to transfer pallets to/from the pivot arm in a machining area and in a working area; a fluid pressure pump for supplying a working fluid to the actuator; a transport mechanism for driving the pivot arm to pivot the pivot arm between the machining area and the working area; a common electric motor for driving the fluid pressure pump and the transport mechanism; and switching means for connecting the electric motor switchably to the fluid pressure pump and to the transport mechanism; wherein one of the fluid pressure pump and the transport mechanism connected to the common electric motor is driven by the common electric motor.
In the automatic pallet changer, the electric motor is first connected to the fluid pressure pump by the switching means for driving the fluid pressure pump. Thus, the actuator is driven to move up the pivot arm, whereby the pallets are received on the pivot arm in the machining area and in the working area. In turn, the switching means switches the connection of the electric motor from the fluid pressure pump to the transport mechanism to connect the electric motor to the transport mechanism for driving the transport mechanism. Thus, the pivot arm is driven to be pivoted, whereby one of the pallets is transported from the machining area to the working area and the other pallet is transported from the working area to the machining area. Thereafter, the electric motor is again connected to the fluid pressure pump by the switching means to drive the fluid pressure pump. Thus, the actuator is driven to move down the pivot arm, whereby the pallets are placed in the machining area and in the working area.
In the automatic pallet changer, the fluid pressure pump and the transport mechanism are individually driven by the single common electric motor, which is switchably connected thereto by the switching means. This eliminates the need for providing separate electric motors for the fluid pressure pump and for the transport mechanism, allowing for size reduction and cost reduction of the automatic pallet changer.
It is preferred to employ a stepping motor as the electric motor and to employ an electro-magnetic clutch as the switching means.